The background information discussed below is presented to better illustrate the novelty and usefulness of the present invention. This background information is not admitted prior art.
All electric utilities and their customers depend on system reliability. In the past, a common means of maintaining system reliability and reducing power outages was through preventative maintenance, which often requires the replacement of specific components after a certain life span, whether the components needed replacement or not. Many utilities have discovered that a better way to maintain system reliability is to practice predictive maintenance, where the emphasis is on finding the failing components, before they cause problems. Additionally, during construction of overhead power lines, it is desirable for electric utilities to have some inspection means of ensuring that the various components used during said construction are assembled correctly. Some of these components that would be desirable to test (whether during construction or as part of a predictive maintenance scheme) are power-line couplings, which include: (i) compression sleeves which join two ends of a power-line cable together and (ii) dead-ends which are utilized on power-line towers where the line changes direction (e.g. from running West to running North).
Industrial radiography is a known method for Non Destructive Testing, or NDT; that is, the material qualities of an object can be examined, tested and studied without destroying the object. For example, photographing the object with the help of gamma radiation makes it possible to discover different material defects such as poor welding seams or cracks. A typical situation in NDT radiography is where a gamma radiation source is being used to inspect a welded seam on a pipe or pipeline.
In gamma radiography, the radiation comes from a radioactive source, such as Iridium-192, for example. The radioactive source is typically placed in a portable protective container during storage and transport. In one design of equipment the source is stored in a block of lead or depleted uranium shielding that has an S-shaped tube-like hole through the block. In the safe position the source is in the center of the block and is attached to a metal wire that extends in both directions, to use the source a guide tube is attached to one side of the device while a drive cable is attached to the other end of the short cable. Using a hand-operated winch the source is then pushed out of the shield (to a radiating position) and along the source guide tube to the tip of the tube to expose the film. The film is usually placed in an appropriate position on the item being testes, e.g. on the section of pipe. Once the film has been sufficiently exposed to the radiation, the source is then cranked back into its fully shielded position.
Due to the radiation, industrial radiography usually has to be carried out outdoors or within shielded enclosures. The surrounding area must then be cordoned off and the radiation dose rate outside the barred area should not exceed certain levels (usually strictly regulated). Since a radioactive source can never be turned off; upon the completion of NDT exposure, the source must be redrawn into its shielded container. The operator must then check with a hand monitor that the source is safely back in its shielded position.
However, trying to adapt the techniques and equipment of industrial radiograph (that works well on pipelines) to overhead electrical power lines and their couplings such as compression sleeves and dead-ends, is problematic. Typically, such overhead lines are 80 feet above the ground, requiring the use of a man-basket lifted by a boom-truck or a crane to provide physical access thereto. This overhead work environment creates safety issues that are not normally found when working on ground level. For example, the radiation source could become stuck or suspended in the radiating position (such as due to a failure of the winch or the drive cable). In a ground level scenario, some lead shielding would simply be placed over the radiation source, while the problem was fixed. However, being suspended on an electrical power-line at a great height above the ground, trying to fully cover an exposed radiation source with lead shielding is highly problematic, if not impossible.
Moreover, the film used in gamma radiography also requires post-exposure chemical processing and developing. This takes time and limits the amount of NDT a person or work crew can do (on power-line compression sleeves and dead-ends) during a work day. The use of film is also problematic in terms of obtaining the appropriate “shots” or photos of the relevant area of the power-line coupling, since it takes time to develop the film and a re-take would slow down overall NDT production significantly.
Furthermore, due to the amount of shielding (often lead) in the protective container and length of drive cable (needed to work with gamma radiography from a safe distance), the typical weight of the equipment is often at least 80 lbs or more. Thus gamma radiography equipment is bulky, heavy and awkward, making it cumbersome and unwieldy to use in an overhead power-line environment.
Therefore, what is needed is a more efficient and safer method, system and apparatus for non-destructive testing (NDT) of overhead electrical power-line cables, sleeves, dead-ends and other couplings.